Post harvest diseases fruits and vegetables - Xavier University ...

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Postharvest Disease Initiation 11
D. PATHOGEN PENETRATION INTO THE HOST
Postharvest pathogens can be divided, according to the timing of their
penetration into the host, into those that penetrate the fruits or
vegetables while still in the field but develop in their tissues only after
harvest, during storage or marketing, and those that initiate penetration
during or after harvest.
1. INFIELD PENETRATION AND QUIESCENT INFECTIONS
Harvesting and Picking after Pathogen Penetration
Late blight of potatoes, caused by Phytophthora infestans, is an
example of decay originating in tuber infection in the field. The infection
is caused by the zoospores found in the soil or that fall onto the tubers
from infected foliage during harvest. Following germination the
zoospores penetrate into the tubers through the "eyes", lenticels, growth
cracks, wounds, or via the point of attachment to the plant (the stolon)
(Lapwood, 1977). Tubers that were infected a few days prior to harvest or
during the harvest itself are brought to storage carrying the disease in its
early developmental stages, with no visible symptoms of decay. These
tubers will decay while stored under high humidity and at a temperature
over 5°C.
In a warm and damp climate, the blight fungus can also attack the
tomato fruit at its various ripening stages, in the field. The attack
usually takes place at the edge of the fruit stalk scar, although, given
prolonged humidity, the fungus can also penetrate directly through the
skin (Eggert, 1970). During epidemics the entire crop may rot in the
field. However, when the disease is less severe, fruits with no visible
symptoms or with slight blemishes might be picked, and the fungus will
continue to develop during storage.
The brown rot, which develops in citrus fruits during storage,
originates in preliminary infections initiated in the orchard by
Phytophthora citrophtora and other Phytophthora species. During the
rainy season, the fungal zoospores descend on the lower fruits on the tree
and penetrate them directly (Feld et al., 1979). The fungus can develop in
the orchard, but when zoospore infection occurs a few days prior to
picking, when the external symptoms are not yet visible, the fruit will
later rot and might comprise a serious problem during storage or
shipping.
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